Keyboard is one of important tools to input signals and communicate with computers. The keyboard has a circuit in response to the computers. The design of the circuit is critical to the quality of the keyboard. The conventional circuit located in the keyboard usually adopts a standard keyboard protocol. The keyboard protocol is serial and provides a specific code for every key except toggle keys (Shift, Ctrl and Alt keys). Referring to FIG. 1 PRIOR ART, the circuit in the keyboard contains a microprocessor 100 which has a plurality of parallel lines and vertical lines 111a, 111b, 112a and 112b that form a matrix 110 to connect to a primary level resistance R1. The matrix 110 crisscrosses to form a plurality of keys 120a, 120b, 120c and 120d. When the key 120a is depressed, the keyboard sends a code representing the key 120a to the computer to be interpreted. When the key 120a returns to the original condition, the keyboard issues a release signal. One cycle of the reciprocal action is treated as one keystroke. When the keyboard is tested the circuit of a preset matrix 110 is used. However, even if all the elements and power supply are in good conditions, a conflict still might happen. This often occurs when a user depresses one key 120a then depresses another key 120b. The system issues the signal of the second key rather than the signals of the two keys. This is because the keyboard codes are mutually exclusive. The preceding signal is masked by the succeeding signal and not recovered.
Another phenomenon occurs when the user depresses two keys 120a and 120b on the rectangular angles of the matrix 110 of the keyboard circuit, then depresses another key 120c (or 120d). The microprocessor 100 cannot accurately determine the signal of the another key 120c (or 120d). This phenomenon is called ghost key. This problem could result in loss of characters when the user depresses the keys at a fast speed. For game players who use the keyboard, they often depress a plurality of keys at the same time to generate toggle key signals to execute different game strategies. The ghost key phenomenon of the keyboard makes the game not be able to be executed smoothly.
To prevent the problem of ghost key when users depress the keys but no effective signal have been generated, R.O.C. patent publication No. 00486661 entitled “Input device using keys defined by multi-dimensional electrodes and coding method thereof” provides a technique to inspect whether a ghost key (or called phantom key) has been depressed. An error signal is sent back. It includes electrodes of N-dimension to define every key on the input device. N is an integer greater than 2. It adopts a key scanning method which scans the electrode of every dimension and records their position data to do comparison and find out the keys being depressed.
R.O.C. patent publication No. 00578088 entitled “Keyboard input device equipped with Blair input function” discloses a simple keyboard to avoid generating ghost keys. It has a simple keystroke input function and the Blair input function. The keyboard includes an input circuit in a key matrix form. On the key matrix, no two keys designated with the Blair input function are connected to a same scanning line. When the input device is using the Blair input function, six keys that are designated with Blair input function can be operated simultaneously in a six-point input system without generating a phantom key on any of the designated keys.